The study was carried out by a research group in Scotland. They looked at people’s responses to different smiles. They found that responses changed greatly.

Through this they have【小题1】 that three types of smiles do not work well: The first is ‘The Enthusiast’（热情过度者），very wide, all teeth showing, possible proof that you can have too much of a good thing. Then there is the ‘Big freeze’, a fixed smile that looks practiced and 【小题2】. Finally comes ‘The Robot’, a small, thin smile without any 【小题3】 .

The group also warns about smiling too quickly, saying it can make you look insincere. The best smile , they say, is slower and floods brightly 【小题4】 the whole face.